High corrosion-resistant high-aluminum zinc-aluminum-magnesium-silicon plated steel sheet and method for manufacturing the same

Abstract

The present application relates to a kind of high corrosion resistance high-aluminum zinc-aluminum magnesium silicon coating steel plate and its manufacturing method, in coating, in the multi-component phase of aluminum-zinc dendrite gap, according to the total area occupied by aluminum-zinc dendrite gap: MgZn2 intermetallic compound accounts for 10%~20%, Mg2Si intermetallic compound accounts for 2%~5%, Zn-Al-Mg ternary eutectic structure accounts for more than 60%.The present application aims to improve the surface and edge corrosion resistance of high-aluminum zinc-aluminum magnesium silicon coating steel plate.By component optimization and process parameter setting, form reasonable coating organization and form, further improve the corrosion resistance of coating.

Description

Technical Field

[0001] This invention belongs to the field of hot-dip galvanizing technology and relates to a high corrosion-resistant, high-alumina zinc-aluminum-magnesium-silicon coated steel sheet and its manufacturing method. Background Technology

[0002] Due to the excellent corrosion resistance and aesthetically pleasing zinc flower appearance of hot-dip aluminum-zinc coatings, they are widely used in home appliances, construction, and other fields. In recent years, with increasing environmental awareness, the requirements for corrosion resistance and stability of products have become even more stringent, leading to the development of high-aluminum zinc-aluminum-magnesium coated steel sheets. These sheets further enhance the corrosion resistance of the coating by adding a certain amount of magnesium to the original aluminum-zinc coating.

[0003] While aluminum-zinc coatings exhibit strong surface corrosion resistance, their high aluminum content means their corrosion resistance primarily relies on the barrier effect of the alumina film. Once this film is damaged, corrosion resistance significantly decreases. Furthermore, aluminum-zinc coatings have poor resistance to edge corrosion, mainly because aluminum's corrosion mechanism prevents it from flowing or forming well-sealed corrosion products. This is especially problematic when cutting thicker plates; exposed steel edges often develop red rust first, subsequently corroding the entire part and causing material failure, particularly in areas requiring interlocking. Although zinc in aluminum-zinc coatings can undergo sacrificial corrosion, its flowability at edges remains poor, and the resulting corrosion products are primarily zinc oxide. These products have poor adhesion and are easily peeled off, failing to protect exposed steel edges.

[0004] Adding a small amount of magnesium to the aluminum-zinc coating causes the formation of a zinc-aluminum-magnesium-silicon alloy phase between the aluminum-zinc dendrites. Under corrosive conditions, this phase forms flowable and dense corrosion products, which can better delay the corrosion failure of the coating. Especially at the cut edges, the corrosion products can have a wrapping effect on the exposed steel substrate, preventing the steel substrate from being corroded and failing.

[0005] The addition of magnesium transforms the original zinc-rich phase and silicon particles between aluminum-zinc dendrites into a zinc-aluminum-magnesium-silicon composite phase. Since the melting points of zinc and magnesium are lower than those of aluminum, the aluminum-zinc dendrites solidify first in the process, and the zinc and magnesium are squeezed into the dendrites to form magnesium-zinc intermetallic compounds, magnesium-silicon intermetallic compounds, zinc-aluminum-magnesium ternary phases, and zinc-rich phases.

[0006] The state and composition of the aluminum-rich dendrites are almost identical to those of the original aluminum-zinc coating. However, the improvement in corrosion resistance, especially the ability to protect the cut edges, depends entirely on the amount of magnesium and the morphology of the zinc-aluminum-magnesium-silicon composite phase. Through reasonable control, not only can silicon particles form magnesium-silicon intermetallic compounds, but magnesium-zinc intermetallic compounds can also be generated simultaneously. Furthermore, a large amount of zinc-aluminum-magnesium eutectic structure that can flow after corrosion can be produced, which plays a significant role in protecting the cut edges.

[0007] In current production and applications, unreasonable component design and process control often lead to problems such as blackening of the coating surface, increased black spots, and inability to improve edge corrosion resistance. This invention aims to prepare aluminum-zinc-magnesium-silicon coating products with superior corrosion resistance through component optimization and process parameter setting, which significantly improves both surface corrosion resistance and edge corrosion resistance. Summary of the Invention

[0008] The purpose of this invention is to provide a high-corrosion-resistant high-alumina zinc-aluminum-magnesium-silicon coated steel sheet and its manufacturing method, aiming to improve the surface and edge corrosion resistance of the high-alumina zinc-aluminum-magnesium-silicon coated steel sheet. Through composition optimization and process parameter setting, a reasonable coating structure and morphology are formed, further improving the corrosion resistance of the coating.

[0009] To achieve the above objectives, the present invention employs the following technical solution:

[0010] A high corrosion-resistant, high-alumina zinc-aluminum-magnesium-silicon coated steel sheet, wherein, in the multi-component phase of the aluminum-zinc dendrite interstices, calculated by the total area occupied by the aluminum-zinc dendrite interstices: MgZn2 intermetallic compounds account for 10%–20%, Mg2Si intermetallic compounds account for 2%–5%, Zn-Al-Mg ternary eutectic structure accounts for more than 60%, and the remainder consists of zinc-rich particles, aluminum-rich particles, and trace rare earth particles.

[0011] Within the interdendritic region of the aluminum-zinc coating, the Mg content is 4wt%–8wt%, the Zn content is 60wt%–80wt%, the Si content is 0.6wt%–1.2wt%, the Al content is 10wt%–30wt%, the total rare earth element (RE) is 0.05wt%–0.15wt%, and the Fe content is 1.0wt%–2.5wt%.

[0012] In terms of area, aluminum-zinc dendrites account for 75% to 85% of the total area of ​​the coating. The dendrites are composed of zinc-rich phases, magnesium-zinc intermetallic compounds, magnesium-silicon intermetallic compounds, and zinc-aluminum-magnesium ternary eutectic alloy phases.

[0013] The overall coating contains Mg content of 1.1wt% to 2.0wt%, Zn content of 30wt% to 45wt%, Si content of 1.0wt% to 1.7wt%, total rare earth element (RE) content of 0.05wt% to 0.15wt%, Fe content of 1.0wt% to 2.5wt%, and the remainder is Al and unavoidable impurities.

[0014] A method for manufacturing a high corrosion-resistant, high-aluminum zinc-aluminum-magnesium-silicon coated steel sheet, wherein after the strip exits the hot-dip galvanizing bath and passes through an air knife, the cooling rate in the first cooling zone is 15-30℃ / s, the cooling rate in the second cooling zone is 8-15℃ / s, the temperature of the strip reaching the upper top roll is below 300℃, and the temperature of the strip entering the water quenching tank is below 120℃.

[0015] The temperature of the zinc-aluminum-magnesium-silicon plating bath is 580-600℃, the temperature of the steel plate entering the hot-dip galvanizing bath is 560-590℃, the height of the air knife is 200-800mm, and the distance between the air knives is 5-30mm.

[0016] The hot-dip galvanizing solution contains 0.8wt% to 1.6wt% Mg, 30wt% to 45wt% Zn, 1.0wt% to 1.7wt% Si, 0.05wt% to 0.15wt% total rare earth element (RE), 1.5wt% to 3.0wt% Fe, and the remainder is Al and unavoidable impurities.

[0017] In aluminum-zinc coatings, the high aluminum content forms an alumina film, resulting in strong surface corrosion resistance. Corrosion often begins in the interdendritic gaps between aluminum and zinc. Replacing the zinc-rich phase in the original aluminum-zinc coating with ternary eutectic phases of Mg-Zn, Mg-Si, and Zn-Al-Mg can greatly improve the corrosion resistance of the interdendritic gaps. In particular, the corrosion products exhibit good adhesion and are dense, thus alleviating further corrosion of the coating.

[0018] As an intermetallic compound, the MgZn2 phase has strong corrosion resistance, but if its content is too low, it provides poor protection for dendrite interstices, and if its content is too high, it is a brittle phase that is prone to severe intergranular fracture during forming. Therefore, the content is controlled at 10% to 20% in this invention. The zinc-aluminum-magnesium ternary eutectic structure accounts for more than 60%, which mainly generates viscous and dense corrosion products in the ternary phase corrosion environment, effectively preventing further erosion of the coating by the corrosive medium. If the proportion of the ternary eutectic phase is small, the number of zinc-rich particles increases, resulting in more ZnO particles that are easy to detach in the corrosion environment, thus reducing corrosion resistance. The addition of Mg causes most of the original Si particles to form the Mg2Si phase, which not only increases the coating strength but also inhibits the local stress concentration of the original Si particles under deformation conditions.

[0019] The Mg content in the finished coating is between 1.1wt% and 2.0wt%, while the Mg content in the interdendritic spaces reaches 4wt% to 8wt%. This is mainly achieved by controlling the post-plating cooling process, which allows the aluminum-zinc rich dendrites to cool rapidly and displace elements such as Mg and Zn into the interdendritic spaces.

[0020] During the post-plating cooling process, the first cooling zone (the first cooling zone after hot-dip galvanizing, where the steel plate passes through the air knife) has a faster cooling rate of 15-30℃ / s. This is mainly to allow the primary and secondary dendrites of aluminum-rich zinc to solidify quickly and to fully displace Mg elements into the dendrite interstices, increasing the Mg content in the interstices and promoting the formation of a larger proportion of Mg-Zn phase and zinc-aluminum-magnesium ternary eutectic phase.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] A high corrosion-resistant high-aluminum zinc-aluminum-magnesium-silicon coated steel sheet and its manufacturing method are disclosed. By adjusting the composition and process, the element distribution and microstructure of the coating are made to form a state that is conducive to corrosion resistance. The resulting microstructure can significantly improve the corrosion resistance of the coating, especially the corrosion resistance at the cut edges. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the microstructure of the high-alumina aluminum-zinc-magnesium-silicon coating of the present invention.

[0024] Figure 2 This is a schematic diagram of the interstitial phase structure between aluminum-zinc dendrites.

[0025] In the figure: 1 - secondary aluminum-zinc rich dendrites, 2 - primary aluminum-zinc rich dendrites, 3 - interstitial phase between aluminum-zinc dendrites. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the specific implementation methods of this invention will be further described below in conjunction with the embodiments. The following embodiments are used to specifically illustrate the content of this invention. These embodiments are only general descriptions of the content of this invention and do not limit the content of this invention.

[0027] The phase composition in the dendrite interstitial space of the present invention is shown in Table 1, the element content in the dendrite interstitial space of the present invention is shown in Table 2, the element content in the overall coating of the present invention is shown in Table 3, the post-coating cooling process of the present invention is shown in Table 4, the hot-dip galvanizing process control parameters of the present invention are shown in Table 5, and the corrosion resistance test of the present invention is shown in Table 6.

[0028] Table 1. Phase composition in dendrite interstitial spaces (%)

[0029]

[0030] In Examples 1-5, aluminum-zinc dendrites account for 75% to 85% of the total area of ​​the coating.

[0031] Table 2. Element content (wt%) in dendrite interstitials

[0032] Mg Zn Si Al RE Fe Example 1 4.1 68 0.81 26 0.06 1.03 Example 2 4.6 69 0.62 24 0.08 1.70 Example 3 5.7 72 1.11 27 0.11 1.08 Example 4 7.1 78 1.02 12 0.15 1.63 Example 5 8 77 0.89 12 0.09 1.00

[0033] Table 3. wt% of the total element content in the coating.

[0034] Mg Zn Si Fe RE Al Example 1 1.3 33 1.16 1.05 0.06 margin Example 2 1.5 37 1.68 1.69 0.08 margin Example 3 1.1 43 1.13 1.11 0.12 margin Example 4 1.6 42 1.02 1.63 0.15 margin Example 5 1.8 39 1.43 1.05 0.08 margin

[0035] Table 4. Control of Cooling Rate After Plating

[0036]

[0037]

[0038] Table 5. Partial Control Parameters of Hot-Dip Galvanizing Process

[0039]

[0040] Table 6. Measurement of coating corrosion resistance: Salt spray corrosion performance (5% NaCl spray, chamber temperature 35±2℃)

[0041]

Claims

1. A high corrosion-resistant high-aluminum zinc-aluminum-magnesium-silicon plated steel sheet, characterized by comprising: In the multicomponent phase of the aluminum-zinc dendrite interstice in the coating, the MgZn2 intermetallic compound accounts for 10-20% of the total area of the aluminum-zinc dendrite interstice, the Mg2Si intermetallic compound accounts for 2-5%, and the Zn-Al-Mg ternary eutectic structure accounts for more than 60%.

2. The high corrosion-resistant high-aluminum zinc-aluminum-magnesium-silicon plated steel sheet according to claim 1, characterized by, In the aluminum-zinc dendrite interstice region of the coating, the Mg content is 4-8 wt%, the Zn content is 60-80 wt%, the Si content is 0.6-1.2 wt%, the Al content is 10-30 wt%, the RE content is 0.05-0.15 wt%, and the Fe content is 1.0-2.5 wt%.

3. The high corrosion-resistant high-aluminum zinc-aluminum-magnesium-silicon plated steel sheet according to claim 1, characterized by, According to the area calculation, the aluminum-zinc dendrite accounts for 75-85% of the total area of the coating.

4. The high corrosion-resistant high-aluminum zinc-aluminum-magnesium-silicon plated steel sheet according to any one of claims 1 to 3, characterized by, In the overall coating, the Mg content is 1.1-2.0 wt%, the Zn content is 30-45 wt%, the Si content is 1.0-1.7 wt%, the RE content is 0.05-0.15 wt%, the Fe content is 1.0-2.5 wt%, and the rest is Al and unavoidable impurities.

5. A method of producing a high corrosion-resistant high-aluminum zinc-aluminum-magnesium-silicon plated steel sheet according to any one of claims 1 to 4, characterized by, The cooling speed of the strip steel in the first cold zone after passing through the air knife of the hot-dip tank is 15-30℃ / s, the cooling speed in the second cold zone is 8-15℃ / s, the temperature of the strip steel to the top roller is lower than 300℃, and the temperature of the strip steel into the water quenching tank is lower than 120℃.

6. The method of producing a high corrosion-resistant high-aluminum zinc-aluminum-magnesium-silicon plated steel sheet according to claim 5, characterized by, The temperature of the zinc-aluminum-magnesium-silicon plating solution is 580-600℃, the temperature of the steel plate into the hot-dip tank is 560-590℃, the height of the air knife is 200-800mm, and the distance of the air knife is 5-30mm.

7. The method of claim 5, wherein the high corrosion-resistant high-aluminum zinc-aluminum-magnesium-silicon plated steel sheet is characterized by The composition of the zinc-aluminum-magnesium-silicon plating solution is as follows: Mg 0.8-1.6 wt%, Zn 30-45 wt%, Si 1.0-1.7 wt%, rare earth 0.05-0.15 wt%, Fe 1.5-3.0 wt%, and the rest is Al and unavoidable impurities.

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